The RADARSAT Constellation is the evolution of the RADARSAT Program with the objective of ensuring C-band data continuity, enhanced operational use of Synthetic Aperture Radar (SAR) data and improved system reliability over the next decade.

Characteristics
The baseline mission includes three satellites, but the constellation is designed to be scalable to six satellites. This allows the system to address future requirements as they arise with greater flexibility. For example, new functionality could be added to a fourth satellite and these functions could be made available to all constellation users. In this fashion, RADARSAT Constellation is a paradigm shift from earlier RADARSAT missions. Instead of launching a single satellite, the capabilities of the system are distributed across several satellites, increasing revisit, and introducing a more robust, flexible system that can be maintained at lower cost and launched into orbit using smaller, less expensive launch vehicles.
The greatly enhanced temporal revisit combined with accurate orbital control will enable advanced interferometric applications in between satellites on a four-day cycle that will allow the generation of very accurate coherent change maps.

Design and Development
The RADARSAT Constellation mission will ensure C-band data continuity for RADARSAT users, as well as adding a new series of applications enabled through the constellation approach. The first satellite of the constellation will be launched to ensure that there is no data gap at RADARSAT-2 end of life. The system does not aim to reproduce RADARSAT-2, but rather to meet core demands at better value for money, and enable new applications. The mission development was started in 2005, with satellite launches planned for 2014 and 2015.

Main Applications
The RADARSAT Constellation mission is being designed for three main uses:

In addition to these core user areas, there are expected to be a wide range of ad hoc uses of RADARSAT Constellation data in many different government applications, federally and provincially, and in the private sector, both in Canada and internationally.

For example, while the mission design initially focused on maritime security requirements, land security, particularly in the Arctic, will be dramatically enhanced. The system offers up to four passes per day in Canadas far north, and several passes per day over the Northwest Passage.

The increase in revisit frequency introduces a range of applications that are based on regular collection of data and creation of composite images that highlight changes over time. Such applications are particularly useful for monitoring changes such as those induced by climate change, land use evolution, coastal change, urban subsidence and even human impacts on local environments.

The following points list the main areas where the Constellation system will be different from RADARSAT-2:

The Constellation is conceived as a government-owned system, providing a large amount of data to government departments for operational monitoring over wide areas.

The ground segment is driven by requirements for fast data delivery of images acquired over Canada, and for fast tasking over international areas.

The majority of acquisitions in Canada concerns large areas to be covered on seasonal basis and therefore most of the acquisitions can be pre-planned.

Conflicts between main users can be resolved in advance.

Imaging requirements are tailored to cover the areas identified by the government users, including both Canadian imaging and international imaging for Canadian users. Allocations are made for extra imaging capacity that may be used to fulfill international commitments.

Main Operational Modes
The system is designed as a medium resolution mission primarily dedicated to regular monitoring of broad geographic areas. This provides a big picture overview of Canadas land mass and proximate water areas. Combined with higher resolution imagery from foreign missions going forward in the same time-frame, the data are expected to dramatically enhance Canadas ability to manage resources and the environment and improve security by providing an operational surveillance system. The system also includes high resolution modes at 3m and 5m, primarily designed for disaster management. (See Figure 1)

The RADARSAT Constellation payload is being designed to provide a beam mode similar to the RADARSAT-1 ScanSAR narrow, which is referred to in the following as the medium resolution mode. The medium resolution mode, which could be used for wide area coverage, was used to size the antenna dimension and power. Other beam modes (stripmap, high-resolution and low-resolution) are designed to be compatible with the system capabilities determined by the medium resolution mode. Starting from the medium resolution mode, the system can provide the following modes:

High-Resolution Mode, which is simply the natural stripmap mode provided by the SAR. It has a single-look resolution approximately equal to half the antenna length

Very-High Resolution Mode, which can be either a stripmap mode or a spotlight mode

Low-Resolution Mode, which is simply a variant of the medium resolution mode where resolution is reduced in favour of a larger swath

Beam Modes
The three-satellite configuration will provide complete coverage of Canadas land and waters offering an average daily revisit at 50m resolution, as well as a significant coverage of international areas for Canadian and international users. (See Figure 2) It will also offer average daily access to 95 percent of the world. The satellites will be interoperable, enabling tasking from one satellite to the next and will be equally spaced in a 600 km low earth orbit. The constellation has a flexible design, allowing up to six satellites to fly in the same plane.

Data Availability
One of the most important project objectives is to increase data availability to the main operational users of SAR data in Canada. The system will be available when the first satellite will be on orbit then the availability of SAR data will increase as more satellites are launched. Requirements are set to ensure continuity with RADARSAT-2. The project will provide continuity for RADARSAT-1 and RADARSAT-2 users, but the system is not designed to be identical. The mission focuses on core applications and products and the provision of best value for money for the government of Canada. Some advanced features like GMTI mode present on RADARSAT-2 are not included. The system performance requirements (NESZ essentially) and data quality (radiometric accuracy) specified for RADARSAT-1 and 2 are maintained. Some aspects of the data quality that were not originally specified for RADARSAT (like ScanSAR beam discontinuities) are now specified based on experience gained through the RADARSAT mission.

For the main system users, the operations should be simplified. Most of the acquisitions in Canada should be pre-planned and data made available to the users in near real-time. In some cases users will process the data; in other cases, specific products will be made available to user organizations. For non-operational users, the interaction with the system for data ordering and distribution should be similar to what is being implemented for RADARSAT-2. It will be possible to order data from an archive, but long-term archiving of the data will be dealt with separately by the CSAs Framework Data Policy and the practices of user organizations and CCRS.

Coverage, Access and Imaging Time
The design should be such that sufficient volume of data can be collected to enable both Canadian and international applications. Their core needs at the highest level can be summarised as:

Ability to image any disaster location in the world within 24 hours to establish the state of critical infrastructure

Ability to monitor all of Canada for disaster mitigation on a regular basis (monthly to twice-weekly) to assess risks and identify damage prone areas

Regular coverage of Canadas land mass and inland waters, up to several times weekly in critical periods, for resource and ecosystem monitoring

The RADARSAT Constellation shall provide 12 minutes imaging time on average per orbit per satellite, with peak imaging of 20 minutes per orbit per satellite. A significant increase in imaging time for the constellation is possible if more satellites are launched. Analysis is ongoing to determine international imaging requirements and their impact on overall imaging requirements.

Revisit and Re-look
The RADARSAT Constellation shall provide a 4-day exact revisit, allowing coherent change detection using an INSAR mode. The RADARSAT Constellation shall provide an average daily global re-look capability in both medium and high resolution modes. Most of the applications considered required at least daily re-look and an exact revisit once to twice weekly (interferometric change detection applications). Very frequent re-look capability is critical to certain disaster management applications.

Timeliness and Data Latency
The timelines and data latency requirement is highly variable according to the application area. For many ecosystem monitoring applications, data delivered several days or in some cases several weeks later may be sufficient. However, maritime surveillance and disaster monitoring have much more demanding timeliness requirements. For maritime surveillance applications in Canadian and adjacent waters, RADARSAT Constellation shall provide 10 minute data latency from acquisition to delivery of data. For ice monitoring and global and Canadian disaster management applications, RADARSAT Constellation shall provide 2 hour data latency from acquisition to data delivery. For ecosystem monitoring applications, RADARSAT Constellation shall provide 24 hour data latency from acquisition to data delivery.

Space Segment
The Radarsat Constellation Mission Space Segment will consist of a constellation of three satellites in a low-earth orbit. Each of the Spacecraft in the constellation will consist of a Bus and a SAR payload. There is also a secondary payload allocation for a potential Automated Identification System (AIS) for ships, which is not planned as part of the baseline mission and is being considered by DND. The radar payload will perform all imaging operations, store, encrypt and transmit the radar data. (See Figure 5.)
The AIS payload could receive ships messages in a wide swath larger than the accessible swath of the SAR. The Bus module will provide attitude and orbit control, power generation and storage, payload commands, telemetry, thermal control and the primary support structure.

Ground Segment + Operations Concept
The baseline ground segment is based on upgrades to the existing RADARSAT-2 ground segment, using the Gatineau and Prince Albert stations for data reception, the St-Hubert and Saskatoon stations for TT&C, and the Svalbard station as a backup for TT&C and data reception. It will be harmonized for data reception at the Polar Epsilon coastal stations in order to support near-real time maritime surveillance. It will also include a fast tasking capability allowing access to the satellites on every orbit, likely achieved through international partnerships.

Ground Segment
The RADARSAT Constellation will require ground stations with vast coverage over Canadian maritime zones of interest in order to provide data within 10 minutes of acquisition. The ground segment will be based on upgrades to the existing RADARSAT-1 and 2 ground segment, using the Gatineau and Prince Albert stations for reception and the St-Hubert and Saskatoon stations for TT&C. Upgrades will allow basic constellation operations. It will be extended to include upgrades to coastal stations and potential international partnerships in order to support near-real time maritime surveillance. It will also include a fast tasking capability allowing access to the satellites on every orbit, likely achieved through international partnership.

The maritime surveillance requirements are among the most demanding from a mission and system requirement point of view. (See Figure 6.) DND has a requirement to cover three zones extending up to 1,000 nautical miles from the coast, which are shown below. Transport Canada has requirements to detect ships four days before they enter Canadian waters, which involves voluntary disclosure out to 2,000 nautical miles, and imaging out to 1,200 nautical miles.

An important aspect of the system operation is the availability of an Automated Identification System (AIS) payload for ship identification. Using AIS, ships exchange information on their identity, position, course etc. The RADARSAT Constellation spacecraft will carry an AIS receiver to gather information on ships over the zone covered by the SAR payload. The AIS will report most of the ships over the zones of interest.

Launch Segment
Launch Segment will consist of the launcher and launch service provider. The mission will use a single spacecraft / single launcher configuration.The mission planning and spacecraft control functions will be located at St-Hubert.

System Characteristics
Please see Figure 7.

Phase A Accomplishments
The RADADSAT Constellation mission completed its Phase A in 2007. During this phase, the initial design concept was completed based on the User Requirements developed by the Canadian User and Science Team in collaboration with the International User Team. These requirements are meant as guidelines in the conduct of mission definition studies.

In addition, the CSA has drafted a Mission Requirements Document (MRD), which translates user requirements into mission requirements that the industry team must address in designing the mission concept. At the system level, the industry team has drafted a System Requirements Specification (SRS), which translates the higher level mission requirements into detailed system requirements.

Phase B
During Phase B, the design concept was refined and the preliminary design of the satellites completed. CSA continued consultations with other Canadian Government Departments that have a vested interest in this space mission, to ensure that the design effectively responds to their requirements.

A Data Utilization and Plan was drafted early in Phase B to identify required developments for project success. The document covered all aspects of the data utilization, including the new applications enabled by the constellation. A plan for science activities was included in the Data Utilization Plan, which will seek to maintain a balance between the operational applications development and the science applications developments.

Internationally, CSA continued discussions with a number of potential partners to identify collaborations in the following main areas:

Missions interoperability

Data exchange

Use of International ground stations for data reception

CSA is also closely following the evolving developments in the international remote sensing community to identify potential synergies, recognizing how the mission could serve global initiatives that rely on data from advanced Earth observation satellites. See Figure 8 for the constellation project schedule. The final design will be approved in Phase C and the satellites will be manufactured in Phase D. As of this writing, the satellites are planned for launch in 2014 and 2015.

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The Canadian Space Agency (CSA) has set out to ensure that all Canadians learn and benefit from the innovations of space science and technology to the greatest extent possible. Its objectives are to support and promote a highly competitive space industry and address the needs of Canadian society. With almost half of Canadas GDP growth in the knowledge-intensive sectors of the economy, the Canadian Space Program is a key driver behind continued leadership on the world stage, new opportunities for industry and scientists, and long-term social and economic benefits for all Canadians.